#include<bits/stdc++.h>
using namespace std;

#define FOR(i, a, b) for(int i = (a); i < (int)(b); ++i)
#define rep(i, n) FOR(i, 0, n)
#define ALL(v) v.begin(), v.end()
#define REV(v) v.rbegin(), v.rend()
#define MEMSET(v, s) memset(v, s, sizeof(v))
#define UNIQUE(v) (v).erase(unique(ALL(v)), (v).end())
#define MP make_pair
#define MT make_tuple

bool is_prime(int n){
  if (n < 2) return false;
  int i = 2;
  while (i * i <= n) {
    if( n % i == 0){
      return false;
    }
    i++;
  }
  return true;
}

int hashh(int v) {
	while(v>=10) v=v/10+v%10;
	return v;
}

int h[200200];

int main(){

  int K, N;
  cin >> K;
  cin >> N;
  FOR(i, K, N + 1) {
    if(is_prime(i)) {
      h[i] = hashh(i);
    } else {
      h[i] = -1;
    }
  }
  int max_cnt = -1;
  int max_int = -1;
  FOR(i, K, N + 1){
    if(h[i] == -1) continue;
    set<int> st;
    int cnt = 0;
    FOR(j, i, N + 1){
      if(h[j] == -1) continue;
      //cout << h[j] <<  " ";
      st.insert(h[j]);
      cnt++;
      if (st.size() != cnt) break;
    }
    cnt = st.size();
    //cout << endl;
    if(max_cnt <= cnt && i > max_int) {
      max_int = i;
    }
    max_cnt = max(max_cnt, cnt);

  }
  cout << max_int << endl;

  return 0;
}